Air Infiltration vs Insulation: Continuous Air Barrier System Deserves Attention
In a recent article for Green Builder Media, Chris Norris suggests that the energy-saving potential of continuous air barriers is often underrated. For some time, state energy codes focus more on conductive heat transfer through exterior walls than on air leakage. Now, building codes increasingly set air leakage standards as well.
Air Infiltration vs Insulation
Current codes require continuous insulation for frame structures, “In at least six out of eight U.S. climate zones—while there are continuous air barrier requirements in five out of eight climate zones.” Norris contends that it is possible that the real-world benefits of continuous air barriers are not adequately represented by current building requirements.
Norris compares continuous insulation and continuous air barriers from a building science perspective. He uses the results of a case study to promote that the energy-efficiency of a continuous air barrier system is underrated.
More State Codes Address Air Barrier Performance
Canada led the way with quantitative standards for air barrier materials when such products were first included in the country’s national building code in the 1980s. Gradually, an increasing number of states are focusing on quantitative air barrier standards in their codes. In 2001, Massachusetts became the very first US State to employ such an air barrier code. Subsequently, Minnesota, California, Connecticut, Georgia, The District of Columbia, Illinois, Maryland, Massachusetts, Mississippi, New York, Oregon, Rhode Island, and Washington State have followed suit.
Case Study Highlights Air Barrier Performance
In his article, Norris details exacting specifications of the hypothetical baseline commercial structure. The study analyzed air barrier performance in a medium-sized three-story office building variously deployed in three divergent climates, those of Seattle, Toronto and Dallas. The building featured steel stud exterior walls with brick veneer. The building met the minimum ASHRAE 90.1-2004 requirement.
Those engaged in the study used batt insulation in the stud space for Dallas and Seattle. They used continuous insulation for the hypothetical Toronto office building. The baseline air leakage rate in the study was 1.55 cfm/ft2 envelope area at 75 Pa pressure difference.
In example #1, researchers add a continuous two-inch rigid insulation to the baseline design. Those conducting the study found that this type of application did little to improve the structure’s air leakage rate.
In example #2, researchers add a continuous air barrier to the baseline design. The air barrier achieves a demonstrable reduction in air leakage, down to 0.4 CFM/ft2 at 1.57 psf (75 Pa).
Ultimately, this study suggests that adding a continuous air barrier reduces air leakage, and energy consumption in both new and retrofitted structures.
Dörken is a leader in the manufacture of air and moisture control products. For further information regarding the energy savings potential of continuous air barriers, please contact us.